The broad, long-term objective of this proposal is to define the mechanism by which the chemokine SDF1 through activation of its receptor CXCR4, contributes to the revascularization of the regenerating lungs. In particular, we plan to determine as to how left lung pnueomonectomy through upregulation of SDF-1 supports the mobilization and incorporation of pro-angiogenic CXCR4+VEGFR1+ hematopoietic cells thereby promoting neo-angiogenesis of the regenerating right lung. We have shown that VEGF family of angiogenic factors promote recruitment of CD133+VEGFR2+ vascular progenitor cells from bone marrow (BM) to the neo-vessels. Signaling through VEGFR2 is essential for the proliferation and differentiation of vascular progenitors. We have also demonstrated that functional VEGFR1 and CXCR4 are co-expressed on the subsets of hematopoietic progenitors cells, supporting mobilization of these cells from the BM's microenvironment. Recruitment of pro-angiogenic CXCR4+VEGFR1+ cells to the regenerating vessels facilitates incorporation of VEGFR2 into functional vasculature. Mobilization and incorporation of BM-derived progenitor cells is a dynamic process and requires activation of a cascade of molecular events that drives recruitment of these cells from unique BM niches. Angiogenic factors, including Placental Growth Factor (P1GF), which exclusively signals through VEGFR1, induce expression of metalloproteinase-9 (MMP-9), which in turn promote the release of soluble Kit-ligand (sKitL, stem cell factor). Increase in bio-available sKitL enhances cycling and morility of CXCR4+VEGFR1+ cells, setting up the stage for mobilization to the circulation. We have preliminary evidence demonstrating that in mice, left lung pneumonectomy results in mobilization and incorporation of hemangiogenic progenitor cells into regenerating lung. Based on these studies, we hypothesize that the regenerating lung through plasma elevation of SDF-1 and VEGFs support the recruitment of marrow derived pro-angiogenic CXCR4+VEGFR1+ hematopoietic cells thereby facilitating incorporation of VEGFR2+ endothelial cells into functional regenerating lung vasculature. This hypothesis will be tested through studying the following specific aims: 1) Determine the temporal, and spatial recruitment patterns and functional contribution of CXCR4+VEGFR1+ progenitors during lung regeneration and compare their incorporation pattern into mice with diminished hemangiogenic potential including, Idl^TdS"'", P1GF"'", VEGF^/", and VEGFigg"'" mice. 2) Assess the physiological significance of SDF-1 and VEGFs in accelerating lung revascularization through recruitment of CXCR4+VEGFR1+ cells. 3) Evaluate the contribution of BM-derived VEGFR2+, and VEGFR1+CXCR4+ cells to revascularization during lung regeneration. The proposed studies will take advantage of the expertise of Dr. RG Crystal (PI) in lung regeneration and emphysema models and the applicant's experience in hematopoiesis and endothelial cell biology to define the mechanism and identify molecular mediators that support recruitment of CXCR4+VEGFR1+ progenitors thereby supporting regeneration of pulmonary vasculature. These studies will lay the foundation for designing clinical protocols to deliver BM derived cells, including CXCR4-t-VEGFRl+ and VEGFR2+ cells, or to introduce SDF-1 and angiogenic factors, to enhance lung revascularization in patients suffering from emphysema and COPD.